Large data processing applications are often partitioned such that they may be carried out by concurrently operating (parallel) processors, each of which handles a different portion of the problem. Independent of the complexity of the processing application, some data communication networks are challenging due to extensive geographic distribution of the elements supported by that communication network and the density of the data transmitted. In either of these two situations or their combination, efficient communication depends on the ability of the communication network to quickly route data from or to elements supported by the communication network. Speed must be maximized, especially in multi-processing systems having heavy traffic due to data acquisition and exchange, while data integrity and simplicity of transmission to any node, from the user's point of view, are maintained.
Prior art solutions called for a large software processing overhead to parse and interpret communication protocol and message routing at each node of the communication network. These prior art solutions have tended to trade speed in favor of flexibility. Examples of such prior art include the Scalable Coherent Interface (SCI), High Performance Parallel Interface (HIPPI), and Fiber Distributed Data Interface (FDDI).
The SCI approach transfers communication control words, destination addresses and source address, in addition to data in each 80 word communication packet. This imposes a burden of approximately 25% of the available packet space to communication protocol overhead (16 words), and time is spent parsing and interpreting every transmission.
The HIPPI is a simplex high performance communication interface which can transmit 800-1600 Megabits per second over a distance of 25 meters using copper cables. In the HIPPI approach, control lines are combined with data lines limiting the network topography to a static communication network configuration, making the HIPPI approach suitable only for parallel and distributed processing systems which have a static distribution of tasks.
The FDDI is a local area network based on token ring protocol. Information is transferred at the rate of 100 Megabits per second on the FDDI ring in frames that are variable in length. The FDDI provides a bridge between conventional high speed ethernet and high speed fiber optic link. It works such that a backbone FDDI ring connects a local island of ethernet work-group to a similar island located in another part of the network. The FDDI approach requires that control lines, source address, destination addresses, and data travel on the same physical line, thereby imposing burdens similar to the message space and processing time dedicated to communication protocol by the SCI approach and the limitation of a fixed communication network configuration as in the HIPPI approach.
Crossbar switches have also been commercially available for interconnecting general purpose processing nodes. Crossbar switches have a fixed number of input/output ports. A crossbar switch may be programmed such that a message transmitted through the crossbar switch may be coupled from any input port to any specified output port. The limited number of nodes attachable to a single crossbar switch results in a high cost per channel when crossbar switches are applied to a geographically extensive multi-processor system consisting of a large number of parallel processors.
These approaches are unsatisfactory for providing efficient data communication in a geographically extensive multi-processor system. It is preferable for such a system to have the following features. It is preferable that the communication network provide simple node access, from the user's perspective, in a reconfigurable multi-processor system. The communication network should also preferably provide intrinsic flexibility to use any combination of the following: (a) multi drop, flat ribbon cable type communication link for short distances, (b) conventional copper (or similar) cable links with intermediary signal filter/amplifiers between start and end points of data transmission as required to prevent signal degradation and distortion if operating over long distances or in a high electromagnetic noise environment, (c) fiber optic links, (d) segmented point to point communication with the capability to concurrently transfer different data in different communication segments within the system, (e) serial data links, (f) parallel data links, or (g) a combination of any of the above approaches applied to individual communication network subsets within the multi-processor system communication network.
It is also preferable that the communication network provide the highest possible ratio of data transferred to transmission protocol overhead. It is preferred that the communication network facilitate SCI, HIPPI and FDDI interfaces, to other systems. The communication network should also preferably facilitate designer selection of the best type of connection and length for each segment within the communication network and interface(s) with other processing systems in accordance with the requirements of the specific application.
In sum, prior art communication schemes do not satisfactory provide for a high speed, minimal protocol overhead means for efficiently communicating a random burst of high density data within a geographically extensive multi-processor system during data acquisition/exchange modes of operation. A communication system design is needed which maximizes data routing speed while maintaining data integrity.